An adaptive data stream filter removes narrowband interference from the CATV return path prior to these paths being combined in the network. A method for removing narrowband interference from the CATV return path detects potential narrowband interference in real-time and adapts a filter to remove this potential narrowband interference. An exemplary embodiment of the above method uses previously created filters that are combined based on detected interference in an adaptive manner to continually adapt to new interference sources. Another exemplary embodiment of the above method calculates new filter coefficients for the data stream filter based on detected interference. In another embodiment, two filters are operated in a ping-pong manner for each band of interference identified as above threshold. This enables updating of one filter while another filter is performing the data stream filter operation.